The present invention relates to a liquid fuel loading management system, particularly for loading fuel onto aircraft, and to methods for determining total fuel weight loaded and temperature standardized total fuel volume loaded.
Fuel loaded onto aircraft has typically been sold by volume. Correspondingly, inventory and control of aircraft fuel was accomplished using volumetric units. While volume measurement is relatively convenient to use for cost, inventory and control purposes, fuel quantity requirements for military and commercial aviation flights are determined by the weight of the fuel since that determines the energy content of the fuel. Thus, when determining fuel requirements for a given flight, the total weight of fuel required for the flight was computed, the weight of fuel already on board determined (usually by reading the aircraft fuel gauges), and the weight of fuel to be loaded was calculated by subtracting the weight of fuel on board from the total weight of fuel required for the flight. Since aircraft fuel requirements were typically determined by weight and loaded by volume, a conversion was performed to obtain the equivalent volume of fuel from the total fuel weight required. The conversion from weight to volume utilized an average density figure for the fuel obtained by measuring a sample of the fuel or an average density figure furnished by the fuel supplier which was corrected to take the temperature of the fuel at the time of loading into account. With this conversion, however, variations in the actual total weight of fuel loaded of about 2% to 5% occurred due to inaccurate density figures and variations in density from the average density used in the conversion process. Typically, the actual weight of the fuel loaded exceeded the desired weight to ensure that sufficient fuel was loaded. When considering the quantity of fuel loaded on current jumbo jets, particularly for long flights, the additional fuel consumption required to carry the excess fuel can be considerable. For example, a variance of only 1% in the weight of fuel loaded can amount to approximately 5,000 excess pounds of fuel on a jumbo jet fueled for a long flight. Thus, reduction in even the 1% variance in fuel weight can provide significant advantages and is highly desirable.
Systems have been proposed for automatically loading aircraft fuel by weight. One such system provided for measurement of fuel uplifted to the aircraft volumetrically as in the past with an automatic conversion to gravimetric units. In order to convert to gravimetric units, the volume of fuel being uplifted was measured, the average density of the fuel to be uplifted was provided to the system and automatically corrected as a function of the temperature of the fuel being loaded, and a gravimetric figure for the total weight of fuel loaded obtained from the measured volume and the average temperature-corrected density figure. However, the average temperature-corrected density figure used in the conversion was often not accurate and the total weight of the fuel uplifted was still not as accurate as would be desired. This system also utilized a preset for the total weight of fuel to be uplifted which automatically terminated fuel flow when the preset fuel weight was uplifted. The preset was resettable so that a previously preset fuel weight to be uplifted could be cancelled during fueling and a new preset weight entered.
In a proposed system of British Airways, the density of fuel being loaded was measured directly as was the volume of fuel being loaded, and from these measurements, the weight of the fuel loaded was determined.
True and accurate accountability for fuel disbursement by volume requires that the volume of fuel delivered be corrected to a recognized standard, e.g., to 60.degree. F. Due to expansion and contraction of liquid with temperature variations, the volume of a given quantity of fuel will vary by a significant amount. A 20.degree. F. shift in temperature will produce as much as 1.2% error in volume measured. Heretofore, aircraft fuel management systems did not automatically provide for such standardization.
Present aircraft include a number of fuel tanks, and to properly trim such aircraft, fuel is distributed in these fuel tanks according to schedules provided by the aircraft manufacturers. Heretofore, the distribution of the fuel among the individual fuel tanks was manually determined using the fuel distribution schedules.
There is thus a need for an aircraft fuel management system which avoids the drawbacks of prior systems including determining fuel weight from volumetric measure more accurately and automatically accomplishing more functions associated with fueling operations than prior systems.